The present invention generally relates to vessels that contain static or flowing fluids, including conduits such as hydraulic hoses of the types used in mobile machinery, automotive, aerospace, manufacturing, and process equipment. The invention particularly relates to hydraulic hoses equipped with means for sensing the life of the hose in terms of wear, fatigue, and/or other structural breakdown of its components, and means for electrically monitoring the hose to predict a structural failure.
Interest exists in developing methods for consistently predicting the failure of vessels containing fluids, including but not limited to hoses, thereby enabling replacement or repair of the vessel before failure from normal wear and/or quality issues that could result in equipment down time and safety concerns.
A hose 20 of a type known in the art is represented in FIG. 1. The hose 20 is representative of various types of hoses that may be used to contain a flowing or static fluid under high pressure conditions. A particular example is a hydraulic hose that contains a hydraulic fluid whose pressure fluctuates. The hose 20 is represented as having an inner tube 22 that contacts a fluid flowing through the hose 20, four reinforcement layers 24 that strengthen the hose 20, intermediate layers 28 between the reinforcement layers 24, and an outer cover 26 that protects the hose 20 and its interior components. Because the inner tube 22 directly contacts the fluid, the material from which the inner tube 22 is formed must be chemically compatible with the fluid contained by the hose 20. The reinforcement layers 24 promote the strength of the hose 20. Any number of reinforcement layers 24 may be present in the hose 20, and reinforcement layers 24 have been constructed from a variety of materials in a variety of configurations, commonly a spiral metal configuration. If multiple reinforcement layers 24 are used, the intermediate layers 28 (for example, formed of a polymer material) can serve as separation layers between the reinforcement layer 24 to reduce abrasion and wear therebetween.
It is conventional to equip the ends of the hose 20 with fittings to permit connection of the hose 20 to other hoses or equipment in a system containing the hose 20. Typical fittings include a nipple that is forced into the opening of the inner tube 22, and an outer collar or socket that is crimped onto the exterior of the hose 20 and onto a portion of the nipple that protrudes from the hose 20. The socket is typically equipped with barbs that are forced through the outer cover 26 and into an outermost reinforcement layer 24 during crimping to secure the fitting on the hose 20. Close tolerances are required to achieve a fluid-tight seal between the hose 20 and the fitting, necessitating a wide variety of fittings in various sizes for use on hoses of different sizes.
Hydraulic hoses of the type represented in FIG. 1 may fail by a variety of mechanisms, including abrasion, loading, fatigue, and environmental factors relating to the hose as well as its fittings and the fluid therein. Because hydraulic hoses are often subject to cyclic loading as a result of pressure changes during startup, shutdown, and normal operation of a hydraulic system, fatigue is an important factor in the life of hydraulic hoses and their fittings. The fatigue rate can increase markedly as a result of damage to the inner tube 22, reinforcement layers 24, and outer cover 26 of the hose 20, as well as damage to the hose fittings.
An example of a life-sensing hose which uses changes in resistance and/or capacitance to predict component failures was disclosed in U.S. Pat. No. 7,555,936 to Deckard. A wide range of hydraulic hoses is encompassed by Deckard, including hoses suitable for medium pressure applications. The terms “medium pressure hydraulic hose” and “high pressure hydraulic hose” will be used herein as defined by the Society of Automotive Engineers (SAE) Standard J517, which defines specifications such as maximum operating pressures for various types of hydraulic hoses. The structure for low, medium, and high pressure hoses are significantly different, limiting the applicability of this type of technology from directly translating between applications. Low pressure hoses are conventionally composed of fiber-based materials such as Kevlar and polymers, high pressure hoses are conventionally composed of many layers of polymers and spiral wire, and medium pressure hoses generally utilize biaxial braided wire as a primary means of strength. The braided wire may be surrounded by rubber components. For this type of hoses, an additional concentric layer of wire may be added separated by the rubber from the first layer of braided wire, thereby creating a cylindrical parallel plate capacitor. As the hose fatigues, individual wires may begin to break within the circuit and pop out into the rubber layer causing a short or change in the overall capacitance that can be utilized to predict early failure. However in low and high pressure hoses, braided wire is not typically used.
It would be desirable if methods and non-braided wire-based hoses were available that made it possible to not only sense an imminent fatigue failure of a hydraulic hose, but were also capable of predicting when a structural failure of the hose may occur so that the hose can be safely used for its full life span and then replaced before failure, thereby reducing the likelihood that damage occurs to a fluid system containing the hose or the apparatus employing the hose as a result of a catastrophic failure.